It is estimated that ~1 in every 110 children is affected by autism spectrum disorders (ASDs) with devastating consequence to the individual and family along with being an economic burden. There is currently no effective therapy available for ASD and understanding the underlying mechanisms may lead to identification of novel therapeutic targets. Human genome-wide association studies have identified genetic variations that may contribute to ASDs. These studies have established that ASD-associated genes are part of a large functional network involved in synapse formation and signaling. However, the precise physiological role of several of the newly identified candidate genes is still unknown. GRID1 (Glutamate Receptor Ionotropic Delta-1) gene, which codes for the glutamate delta-1 (GluD1) subunit, is one such gene identified as a susceptibility gene for ASDs and schizoaffective disorders. Lower GluD1 expression has also been reported in ASD and schizoaffective disorder patients. Moreover, recent studies have identified a potential role of GluD1 in synapse formation via interaction with presynaptic Neurexin1, which itself is an autism susceptibility gene. These converging findings suggest that GluD1 may be a part of the functional synaptic network that is dysregulated in ASD. Our preliminary data strongly indicates that deletion of GluD1 leads to several behavioral and molecular abnormalities that resemble deficits in human ASD patients. The goal of this proposal is to specifically understand the neural basis of these abnormal behaviors in GluD1 knockout mice. Towards this end we will determine the effect of GluD1 deletion in mouse on spine morphology and synaptic function in the medial prefrontal cortex, which regulates social behaviors and cognitive abilities known to be affected in ASD patients. We have also found that an NMDA receptor agonist D-cycloserine is able to rescue social deficits in GluD1 knockout mouse. We will therefore test whether reversal of synaptic abnormalities in the medial prefrontal cortex underlie the efficacy of D-cycloserine in social deficits. These studies will provide the first evidence for a crucial role of GluD1 in the regulation of synaptic structure and function that eventually modulate behavior and potentially identify a novel therapeutic target for ASD. Additionally, our studies will support the hypothesis that facilitation of activity-dependent mechanisms may have therapeutic value in alleviating ASD phenotype.